The present invention relates generally to alarm and warning systems, and is particularly concerned with a system and method for detecting and tracking movement within an enclosed space such as a building.
Conventional building alarm systems have the primary purpose of detecting an intruder and warning the owner or security agency of the presence of the intruder. These traditional systems simply look for an abnormal event and activate a warning device or transmit a warning signal to a remote station. The alarm system does not normally continue to check or monitor the space when already in the alarm state. These alarm systems are normally installed on the inside of buildings to protect the building or structure from intrusion.
One such conventional alarm system is described in U.S. Pat. No. 5,150,099 of Lineau, which describes a home security system for detecting stationary and moving objects within an area. The system transmits electromagnetic radiation into the monitored space, and senses the amplitude of radiation reflected or refracted off objects in the space. The information generated is compared with a pre-generated template, and the device produces an alarm condition if any variations are found. This system does not have any ability to track movement within a monitored space, but simply generates an alarm when a body not in the pre-generated template is detected.
U.S. Pat. No. 5,786,760 of Suzuki et al. describes an alarm system for both detecting the presence of an intruder, and for deterring the intruder by producing a variable, audible alarm or warning signal. The system utilizes plural transmitters of electromagnetic radiation located outside a building but within a fenced area. The radar system detects and monitors the position of an intruder within the outdoor fenced area, and outputs synthesized human or dog voice sounds at varying levels towards the intruder, so that it appears that the intruder is being approached. This system also does not provide any means for monitoring intruder position within an enclosed space.
U.S. Pat. No. 5,448,501 of Hablov et al. describes a detection system for building surveillance which uses a microwave transmitting/receiving device for radiating microwaves into an area and detecting and conditioning the reflected signal received as a result of individuals within the area. The system includes a method of identifying individuals within a building in order to distinguish authorized persons from unauthorized persons, but does not provide any means for tracking movements of intruders within a building.
Although current building alarm systems mounted within buildings can effectively detect a break-in or the like, they are of little or no help to law enforcement officers arriving on the scene where it is suspected that an intruder is still within the building. They are also of no help in situations where a gunman has barricaded himself within a building, with or without hostages. Therefore, there is a need for a system which would locate and monitor a living being from the exterior of a structure or building and track any movement of that being from region to region within the structure. This system would be particularly useful for police officers or SWAT teams in situations where a gunman has barricaded himself within a building, in some cases with hostages. Currently, officers are not able to determine the exact location of the suspect or suspects in the building, or monitor movement in the building. Internal surveillance cameras may not be present and, even if present, can be disabled by the suspect quite easily. An ability to locate the exact position of the or each suspect in such situations can considerably reduce the risk to both hostages and police officers when officers enter the building.